Process and apparatus for drying fabric by electrical energy



Aug. 23, 1966 w. F. SOUTHWELL 3, PROCESS AND APPARATUS FOR DRYING FABRICBY ELECTRICAL ENERGY Filed May 24, 1965 2 Sheets-Sheet 1 FIG. 4

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FIG. 2

INVENTOR.

WYNDHAM F. SOUTHWELL w. F. SOUTHWELL 3, PROCESS AND APPARATUS FOR DRYINGFABRIC BY ELECTRICAL ENERGY 2 Sheets-Sheet z l l l I I l I J INVENTOR.WYNDHAM F. SOUTHWELL L wysx v A TORNEY Aug. 23, 1966' 'Flled May 24,1963 United States Patent 3,267,584 PROCESS AND APPARATUS FOR DRYINGFABRIC BY ELECTRICAL ENERGY Wyndham F. Southwell, Wilkesboro, N .C.,assignor to L&L Manufacturing, Inc., a corporation of Delaware Filed May24, 1963, Ser. No. 283,027 10 Claims. (Cl. 341) This invention relatesto processes and apparatus for removing moisture from fabrics by theheating effect of molecular disturbance by radio frequency energy toevaporate a desired amount of water therefrom.

The process may be carried out by passing, in a given direction, afabric having a predetermined average moisture content in a givendirection in close proximity to and, preferably and in most instances,in contact with a plurality of alternately disposed negative andpositive electrodes which are spaced along an electrode bed and to whicha radio frequency energy is supplied over parallel branches of acircuit, the electrodes being so arranged that pairs or groups ofelectrodes further along the bed in said direction are successively moreclosely spaced than those less far along'in said direction. In thismanner, the wettest part of the fabric, where the conductivity is thegreatest, is subjected to a less concentrated energy field than it wouldif the electrodes were closer together, thus avoiding burning, and thedrier part of the fabric where the conductivity and the consequenteffectiveness of the drying action is less, is subjected to a moreintense field than it would if the electrodes were further apart, thusexpediting the removal of moisture at this part to an extent consistent,for example, with the need of expediting the entire process of reducingthe moisture content of a forwardly-moving elongated strip of fabric.

It is to be noted that the field strength is lower when the distancebetween the electrodes is greatest, so that burning at the points ofgreatest conductivity in the fabric is avoided, and the temperature ofthe fabric is greatest at the point where it leaves the bed.

Two pairs of electrodes may be used; but, ordinarily an extended seriesof electrodes gives the most satisfactory results. The spacing of theelectrodes may be altered only once in the direction of movement of thefabric along the bed, but preferably the spacing of the electrodes issuccessively reduced at several points therealong.

In accordance with the invention there may be provided an electrode bedof the character above indicated, a radio {frequency oscillator or othersource of suitable radio frequency energy and suitable means to connectthe source with the positive electrodesthe negative electrodes and thesource being grounded, for example and means to cause relative movementof the bed and fabric-as, for example, means to draw the fabric alongthe bed and in contact with the electrodes thereof. The latter meansmay, for example, be an ordinary pair of rollers or may befabric-treating means which has a fabric-advancing effect and whichtreats the fabric of which the moisture content has been reduced, suchfor instance as certain shrinkage control mechanism, one example ofwhich isthe belt mechanism illustrated in the Wehrmann Patent 3,007,223issued November 7, 1961. Desirably the series of electrodes should beginand end with a negative electrode. For example, an electrode bed may beprovided which contains nineteen negative electrodes in alternation withwhich eighteen positive electrodes are provided.

The source of radio frequency energy supply may be of such nature as tobe in the high frequency designation or from 5 megacycles to 30megacycles, for example.

While the invention is applicable to the removal of 3,267,584 PatentedAugust 23, 1 966 moisture from any of a wide variety of fabrics, it isparticularly advantageous for use in the removal of moisture fromtubular knitted fabrics, the expeditious drying of which tends to be amatter of great difficulty, and which are unadapte-d for the drying, byordinary procedures, of the interior thereof to the same extent as theexterior thereof. A particular advantage is present in the drying oftubular knitted fabrics as a preliminary step in a shrinkage controloperation which is especially effective when the fabric contains aparticular percentage of moisture distributed uniformly throughout thethickness of a doube-layer of the flattened tube.

In the instant process, the moisture-reduced fabric, moreover, leavesthe bed heated uniformly to the 212 F. temperature of the evaporatingmoisture which is advantageous in certain subsequent processes of whichshrinkage control processes are an example.

By means of the invention, not only can the moisture content of a fabricbe reduced by a continuous process to a substantially uniform percentagewith respect to the dry weight of the fabric, but the percentage ofmoisture throughout the entire thickness of the fabric can be renderedsubstantially uniform. For example, a fabric containing 25% or moreaverage moisture content may be reduced to from 20% to 10% uniformmoisture content.

In addition, the invention is adapted [for the substantially completeelimination of moisture from fabrics containing up to the maximum amountof moisture they will hold.

Since fabrics are not normally wet with distilled water, the water withwhich the fabric is wet, as it comes from previous treating processes,may, in certain cases, be expected to contain enough dissolved materialto render it suitably conductive, and there may, if desired, be added tothe water additional soluble conductive material such as, for example,sodium chloride or sodium fluoride.

The invention accordingly, comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, and the apparatus embodying features of construction,combination of elements and arrangement of parts which are adapted toeffect such steps, all as exemplified in the following detaileddisclosure, and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following description taken in connectionwith the accompanying drawings, in which:

FIGURE 1 is a partial sectional side view showing in a somewhatdiagrammatic fashion the preferred arrangement of the components of theelectrode bed and showing also a short section of a long strip of fabricbeing moved thereover;

FIG. 2 is a fragmentary top view on an enlarged scale taken on the line2-2 of FIG. 1, and with the fabric removed, showing the manner of theelectrode assembly;

FIG. 3 is an end view on an enlarged scale of the bed taken on the line3--3 of FIG. 1, with the fabric in section;

FIG. 4 is a fragmentary sectional view on an enlarged scale taken on theline 4-4 of FIG. 2 and showing a pozitive electrode connected to anenergy conducting strip; an

FIG. 5 is a circuit diagram showing a preferred RF power sourcearrangement.

In the exemplified construction there is provided an electrode bed 10embodying thirty-seven electrodes, which may consist of aluminum rodseach one inch in diameter and comprising nineteen grounded negativeelectrodes 12 in alternation with which eighteen positive electrodes 14are provided. The first ten electrodes are six inches apart from centerto center, the next nine electrodes are 3 four inches apart, the nextnine electrodes are three inches apart, and the last nine electrodes aretwo inches apart. The electrodes extend between grounded conductiveframe pieces 16 and 18, each negative electrode being fifty-eight incheslong, and each positive electrode being fifty inches long with a coronaring 20 and an insulator 21 at each end. Each negative electrode ismounted on the frame pieces by one-quarter inch conductive screws 22,and each positive electrode by one-quarter inch screws 23 extending intothe insulators 21 only. RF energy is supplied to a longitudinal centralportion of each positive electrode by a conductive plate 24, the plates24 being conductively joined to a conductive strip 26 extending beneaththe bed and electrically connected with a conductive post 28 which iselectrically connected to a source of RF energy indicated generally at30. The plates 24 thus serve to supply equal amounts of energy inparallel. The conductive elements may suitably be made of copper oraluminum. The strip 26 is mounted on insulators 3 1. The negativeelectrodes are grounded thru the frame pieces for connection with thegrounded source.

In the present instance the radio frequency source 30 is adapted tosupply thirty kilowatts of energy at 13.5 meg-acycles which may bereduced to 8 or 9 megacycles by load conductions.

A long strip of fabric 33, exemplified as tubular knitted fabric thesides 34 and 35 of which lie flat against each other, may be drawn overthe bed in contact with the electrodes by means such as illustrated insaid Patent 3,007,- 223, or, as illustrated in the drawings (FIG. 1) forthe sake of simplicity by a pair of rollers 37 and 38. As will be seenfrom the drawings, the fabric 36 is shown in contact with the electrodes12 and 14. The speed of movement of a tubular knitted fabric having adry weight of 2.1 pounds per square yard spread out or 4.2 pounds doublethickness, and containing an average moisture content of thirty percentor lower as it moves onto one end of the bed, may be moved over theexemplified bed at a speed of twenty yards per minute and have itsmoisture content reduced to a uniform moisture content of 15% as itmoves out of the other end of the bed, it being noted that such amoisture content is a desirable one for the preshrinking of knittedcotton fabrics.

- By suitably adjusting the conditions various amounts of moisturecontent in a fabric may be suitably reduced.

In general it is to be noted that with a thirty kilowatt generator andoperating at maximum efliciency 1 /2 pounds of water per minute may beremoved, that 56.7 B.t.u. may be generated per kilowatt, and that 1,134B.t.u. are required to dissipate one pound of water per minute.

- By means of an arrangement such as exemplified, the portion of thefabric which is over the initial portion of the bed will have its highmoisture content (which provides a high conductivity) reduced withoutburning, whereas at later portions of the bed the portions of the fabricwith lower moisture contents (while of less conductivity) will havetheir moisture content reduced efficiently and effectively to provide atthe terminal ends of the bed a desired low uniform moisture contentthruout the fabric.

While any of a variety of types of sources of RF energy may be provided,the particular source 30 (FIG. exemplified comprises an arrangementincluding a main conductor 40 which extends to an RF choke 42 and fromwhich a lead 44 extends to a grounded condenser 45, and a lead 46extends to a resistance 47 whence a lead 48 extends to a metering device49 as shown. A lead 50 extends from lead 48 to .a grounded resistance51. From the choke 42 a lead 52 extends to a condenser 53 from which alead 54 extends to a ganged variable condenser unit 55, whence the lead56, to which the positive electrodes are connected by leads embodyingthe elements 28 and 26 and the conductive plates 24, and the arcsuppressor unit 32 is connected by a lead 57 containing an RF choke 58and from this lead is connected to an RF voltmetering unit 59. From thelead 52 a lead 60 extends to plate 61 of an oscillator tube 62, thefilament 63 of which is connected to a tank coil 64 one end of which isconnected by a lead 66 to the lead 54 and from the other end of which alead 67 extends to a condenser 68 connected to the lead 54 by a lead 69.From the grid 70 of the tube 62 a lead 71 extends to a parasiticsuppressor 72 from which a lead 74 extends. A conductor 75 is connectedto lead 74 and extends to a condenser 76, whereas a grounded conductor77 extends to the same end of the tank coil 64 from which the lead 67extends. The lead 74 is also connected thru two sets of resistances 79and 80 to a grid overload device 81, lead 82, resistance 84, groundedlead 85, resistance 86, lead 88, plate overload device 90, and to mainlead 92. Leads 94 from lead 82, and 95 from lead 88, extend to variableresistances which are connected into the metering device 49 as shown.Leads 96 and 97 bridged by a filtering condenser 98 extend,respectively, from the lead 77 and from the righthand (FIG. 5) side ofthe oscillator tube filament 63, to an oscillator filament transformer.

The terms negative and positive as used herein in connection with theelectrodes 12 and 14 and elsewhere refer to a condition at theparticular instant wherein the RF energy is flowing from the positiveelectrode, as the emitter, and thence thru the moisture containingfabric to the negative as the receiver. These terms are used for thesake of convenience of descriptive identification and not in anarbitrary limiting sense.

Since certain changes in carrying out the above process and theconstructions set forth, which embody the invention, may be made withoutdeparting from its scope, it is intended that all matter contained inthe above description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

I claim:

1. A process of removing moisture from fabric which comprises passing awet fabric in flat form continuously first in contact with a set oflaterally extending negative and positive electrodes spaced a relatively:large distance from each other and subsequently in contact with a setof laterally extending negative and positive electrodes spaced arelatively small distance from each other while supplying heat-producingradio frequency energy over bnanch circuits each including a positiveelectrode and a negative electrode of a set and a portion of saidfabric.

2. A process of removing moisture from fabric which comprises passing awet fabric in contact with a plurality of widely spaced electrodes,thereafter in contact-with a plurality of less widely spaced electrodesand subsequently in contact with a plurality of more closely spaced electrodes .while supplying substantially equal amounts of heat-producingradio frequency energy to branch circuits each including at least a pairof spaced electrodes of each plurality and a portion of the fabric.

3. A process of drying fabric comprising passing a fabric in contactwith a plurality of widely spaced electrodes and thereafter withsuccessive pluralities of successively less widely spaced electrodeswhile supplying substantially equal amounts of high-frequency energyfrom a source of such energy to a-lernate ones of said electrodes,passing such energy thru the fabric and con ducting the energy from theother of said electrodes to said source.

4. A process of drying fabric to a uniform moisture con- 7 tent adaptedfor subsequent treatment, comprising passing a fabric having an averagemoisture content of not substanti ally under 25% in contact with aplurality of widely spaced electrodes and thereafter with successivepluralities of successively less widely spaced electrodes whilesupplying substantially equal amoun'ts 'of high-frequency energy from asource of such energy to, alternate ones of said electrodes, passingsuch energy thru the fabric and conducting the energy from the other ofsaid elec trodes of said source, to reduce the moisture content of saidfabric to from about 20% to about 10%.

5. A process of drying tubular knitted fabric which comprises passing awet tubular knitted-fabric with the flat sides in contact with eachother continuously over a pair of relatively widely spaced electrodeswith one side in electrical contact therewith substantially thruout theWidth thereof and then over a pair of less widely spaced electrodes withone side in electrical contact therewith substantially thruout the widththereof while supplying heat-producing radio frequency energy overbranch circuits including the respective pairs and the fabrictherebetween.

6., Apparatus for reducing the moisture content of a wet fa'briccomprising an electrode bed wherein laterally extended spaced negativeand positive electrodes are spaced a greater amount near one end of saidbed than near the other end of said bed, a source of heat-producingradio frequency energy, conductive means from said source to saidpositive electrodes, means to electrically connect said negativeelectrodes to said source, and means to move a wet fabric along said bedfrom said one end to said other end thereof while in electrical contactwith said electrodes.

7. Apparatus for reducing the moisture content of a wet fabriccomprising an electrode bed wherein laterally extended spaced negativeand positive electrodes are arranged in alternation and wherein thespacing of said electrodes is greater near one end of said bed than nearthe other end of said bed, a source of heat-producing radio frequencyenergy, conductive means from said source to said positive electrodes,means to electrically connect said negative electrodes to said source,and means to move a wet fabric along said bed from one end to said otherend thereof while in contact with said electrodes.

8. Apparatus as in claim 7 wherein said conductive means are arranged toprovide a parallel electrical supply circuit and wherein said energy isfrom 5 megacycles to 30 megacycles.

9. Apparatus as in claim 7 wherein the spacing of certain intermediateelectrodes is less than the spacing of those near said one end andgreater than the spacing of those near said other end.

10. Apparatus for reducing the moisture content of a Wet fabriccomprising an electrode bed wherein laterally extended spaced negativeand positive electrodes are arranged in alternation, and wherein thespacing of said electrodes is greater near one end of said bed than nearthe other end of said bed, grounded conductive electrode frame piecesarranged to support the ends of said electrodes, means for conductivelymounting the negative electrodes on the frame pieces, means fornon-conductively mounting the positive electrodes on said frame pieces,a source of high-frequency energy, conductive means from said source tothe intermediate portion of each positive electrode, conductive meansfrom said source than said frame pieces to the conductively-mountednegative electrodes, and means to transport a wet fabric along said bedin electrical contact with said electrodes to provide a moistureconductive path thru said fabric.

References Cited by the Examiner UNITED STATES PATENTS 2,288,269 6/ 1942Crandall 341 2,473,251 6/1949 Hsu 34-1 2,492,187 12/1949 Rusca 34--12,503,779 4/1950 Story 21910.61 2,512,311 6/1950 Davis 341 2,588,8113/1952 Dippel et al. 34-4 JOHN J. CAMBY, Primary Examiner.

NORMAN YUDKOFF, Examiner.

F. E. DRUMMOND, Assistant Examiner.

5. A PROCESS OF DRYING TUBULAR KNITTED FABRIC WHICH COMPRISES PASSING AWET TUBULAR KNITTED FABRIC WITH THE FLAT SIDES IN CONTACT WITH EACHOTHER CONTINUOUSLY OVER A PAIR OF RELATIVELY WIDELY SPACED ELECTRODESWITH ONE SIDE IN ELECTRICAL CONTACT THEREWITH SUBSTANTIALLY THRUOUT THEWIDTH THEREOF AND THEN OVER A PAIR OF LESS WIDELY SPACED ELECTRODES WITHONE SIDE IN ELECTRICAL CONTACT THEREWITH SUBSTANTIALLY THRUOUT THE WIDTHTHEREOF WHILE SUPPLYING HEAT-PRODUCING RADIO FREQUENCY ENERGY OVERBRANCH CIRCUITS INCLUDING THE RESPECTIVE PAIRS AND THE FABRICTHEREBETWEEN.